WO2019181142A1

WO2019181142A1 - Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and light sensor

Info

Publication number: WO2019181142A1
Application number: PCT/JP2018/048440
Authority: WO
Inventors: 真寛足立; 光太郎廣瀬; 木山　誠; 松浦　尚; 喜之山本; 恒博竹内; 俊佑西野
Original assignee: 住友電気工業株式会社; 学校法人トヨタ学園
Priority date: 2018-03-20
Filing date: 2018-12-28
Publication date: 2019-09-26

Abstract

A thermoelectric conversion material including: a base material being a semiconductor comprising a base material element; a first additive element that is a different element from the base material element, has a spare d orbit or f orbit positioned on the inside of the outermost shell thereof, and forms a first additional level inside a forbidden band of the base material; and a second additive element that is different from both the base material element and the first additive element and forms a second additional level inside the forbidden band of the base material. The difference between the number of electrons in the outermost shell of the second additive element and the number of electrons in the outmost shell of at least one base material element is 1.

Description

Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and optical sensor

The present disclosure relates to a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, and an optical sensor.

This application claims priority based on Japanese application No. 2018-53183 filed on Mar. 20, 2018 and international application PCT / JP2018 / 032583 filed on Sep. 3, 2018. All the descriptions described in the above are incorporated.

As a thermoelectric conversion material, a technique has been reported in which a laminate obtained after laminating Si, Ge, and Au is heat-treated to form Au nanoparticles in SiGe (silicon germanium) (for example, Non-Patent Document 1). ). A technique using Si / GeB as a thermoelectric conversion material has been reported (for example, Non-Patent Document 2).

Patent Document 1 discloses a thermoelectric conversion material including nanoparticles containing a base material element and a different element different from the base material element in a base material made of a semiconductor material composed of the base material element.

International Publication No. 2014/196475

The thermoelectric conversion material according to the present disclosure includes a base material that is a semiconductor composed of a base material element, and an element different from the base material element, and has an empty orbit in a d or f orbit located inside the outermost shell. A first additive element that forms a first additional level in the forbidden band of the base material, and an element different from both the base material element and the first additive element, and the second additive element in the forbidden band of the base material. And a second additive element that forms an additional level. The difference between the number of electrons in the outermost shell of the second additive element and the number of electrons in the outermost shell of at least one of the matrix elements is 1.

FIG. 1 is a graph showing the relationship between the value of ZT and the content ratio of Au. FIG. 2 is a schematic diagram showing the energy state of the thermoelectric conversion material when it contains the first additive element. FIG. 3 is a schematic diagram showing an energy state of the thermoelectric conversion material according to Embodiment 1. FIG. 4 is a diagram showing energy levels formed by each element as the first additive element substituted with Si and Ge when the base material is SiGe. FIG. 5 is a schematic view showing the state of the structure of the thermoelectric conversion material in the second embodiment. FIG. 6 is a graph showing the relationship between the temperature of the thermoelectric conversion material and ZT in the second embodiment. FIG. 7 is an X-ray diffraction pattern of the thermoelectric conversion material in the second embodiment. FIG. 8 is a graph showing the density of states when the content ratio of Re added as the first additive element to MnSi is changed. FIG. 9 is a graph showing the density of states when the content ratio of Re added as the first additive element to MnSi is changed. FIG. 10 is a diagram illustrating an example of a band structure in the case where the first added level of Sc as the first additive element exists in the SnSe-based material. FIG. 11 is a diagram illustrating an example of a band structure in the case where the first added level of Ti and Zr as the first additive element exists in the SnSe-based material. FIG. 12 is a diagram illustrating an example of a band structure in the case where the first additional level of Sc, Ti, and V as the first additive element exists in the Cu ₂ Se-based material. FIG. 13 is a diagram illustrating an example of a band structure in the case where the first added level of Co and Ni as the first additive element exists in the SnSe-based material. FIG. 14 is a schematic diagram showing a structure of a π-type thermoelectric conversion element (power generation element) that is a thermoelectric conversion element in the sixth embodiment. FIG. 15 is a diagram illustrating an example of the structure of the power generation module. FIG. 16 is a diagram illustrating an example of the structure of an infrared sensor.

In recent years, renewable energy has attracted attention as a clean energy alternative to fossil fuels such as oil. Renewable energy includes not only power generation using sunlight, hydropower and wind power, but also energy generated by thermoelectric conversion using temperature differences. In thermoelectric conversion, since heat is directly converted into electricity, no extra waste is discharged during the conversion. Since thermoelectric conversion does not require a driving unit such as a motor, it has a feature such as easy maintenance of the apparatus.

The conversion efficiency η of temperature difference (thermal energy) using a material (thermoelectric conversion material) for performing thermoelectric conversion is given by the following formula (1).

_{η = ΔT / T h · (} M-1) / (M + T c / T h) ··· (1)
η is the conversion efficiency, [Delta] T is the difference between _{T h} and _{T c,} _{T h} is the temperature of the high temperature side, _{T c} is the cold side temperature, M is ^{(1 + ZT) 1/2, ZT} = α 2 ST / κ, ZT Is a dimensionless figure of merit, α is the Seebeck coefficient, S is the conductivity, and κ is the thermal conductivity. Conversion efficiency is a monotonically increasing function of ZT. Increasing ZT is important in the development of thermoelectric conversion materials.

[Problems to be solved by the present disclosure]
A thermoelectric conversion material having higher conversion efficiency than the thermoelectric conversion materials disclosed in Non-Patent Document 1, Non-Patent Document 2 and Patent Document 1 is required. If ZT can be increased, the efficiency of thermoelectric conversion can be improved.

Therefore, it is an object to provide a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, and an optical sensor that have improved thermoelectric conversion efficiency.

[Effects of the present disclosure]
According to the thermoelectric conversion material, the efficiency of thermoelectric conversion can be improved.

[Description of Embodiment of Present Invention]
First, embodiments of the present application will be listed and described. The thermoelectric conversion material according to the present application is a base material which is a semiconductor composed of a base material element and an element different from the base material element, and has an empty orbit in a d orbit or f orbit located inside the outermost shell. The first additive element that forms the first additional level in the forbidden band of the material, and an element different from both the base material element and the first additive element, and the second additional element in the forbidden band of the base material And a second additive element that forms a level. The difference between the number of electrons in the outermost shell of the second additive element and the number of electrons in the outermost shell of at least one of the matrix elements is 1.

The thermoelectric conversion material includes a base material that is a semiconductor composed of a base element. Since a semiconductor has a larger band gap than a conductive material, the Seebeck coefficient can be increased. As a result, the dimensionless figure of merit ZT can be increased by adopting the base material.

The thermoelectric conversion material can form the first additional level in the forbidden band of the base material as a new level by including the first additive element. Since the first additive element has an empty orbit in the d orbit or f orbit located inside the outermost shell, the energy width of the first additional level can be reduced. Therefore, the conductivity can be increased despite the high Seebeck coefficient. The thermoelectric conversion material is an element different from both the base material element and the first additive element, and includes a second additive element that forms a second additional level in the forbidden band of the base material. The difference between the number of electrons in the outermost shell of the second additive element and the number of electrons in the outermost shell of the base material element is 1. Therefore, the Fermi level can be controlled by forming an acceptor level or a donor level due to the second additional level formed by the second additive element. As a result, ZT can be increased more reliably and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material described above, the structure of the thermoelectric conversion material may include a crystal phase made of a base material element having a particle size of 50 nm or less. Since the crystal phase has a higher conductivity than the amorphous phase, ZT increases. On the other hand, when the grain size of the crystal phase becomes too large, the thermal conductivity tends to increase. An increase in thermal conductivity can be suppressed by setting the grain size of the crystal phase composed of the base material element to 50 nm or less. Therefore, according to such a thermoelectric conversion material, an increase in thermal conductivity can be suppressed while improving electrical conductivity. Therefore, the efficiency of thermoelectric conversion can be further improved by increasing ZT. The particle size may be 25 nm or less. In this case, an increase in thermal conductivity can be further suppressed. Further, by setting the particle size to 20 nm, it is possible to further suppress an increase in thermal conductivity.

In the X-ray diffraction pattern of the thermoelectric conversion material, at least one of the first additive element and the second additive element with respect to the intensity of the peak having the maximum intensity among the peaks showing the crystal phase composed of the matrix element The ratio of the intensity of the peak having the maximum intensity among the peaks showing the crystal phase including one may be 2.0% or less. In the thermoelectric conversion material, when a large amount of the crystal phase containing at least one of the first additive element and the second additive element is precipitated, the carrier concentration is reduced compared to the case where the crystal phase is small, and the Fermi level is reduced. The position of the position is shifted or the density of the first additional level is lowered. The effect of forming the first additional level and the effect of forming the second additional level are difficult to obtain due to at least one of these factors or both factors. According to the thermoelectric conversion material, since the precipitation amount of the first additive element as a crystal phase and the precipitation amount of the second additive element as a crystal phase is small, the formation of the first additional level by the first additive element The effect and the effect of forming the second additional level by the second additive element can be obtained more reliably. Therefore, the efficiency of thermoelectric conversion can be further improved. The above-mentioned strength ratio is preferably 1.0% or less, more preferably 0.5% or less, and further preferably 0.0%.

In the thermoelectric conversion material, the content ratio of the crystal phase containing at least one of the first additive element and the second additive element with respect to the entire structure of the thermoelectric conversion material is 6.0% by volume or less. Also good. Since such a thermoelectric conversion material has a small amount of precipitation as a crystal phase of the first additive element and a crystal phase of the second additive element, formation of the first additional level by the first additive element And the effect of forming the second additional level by the second additive element can be obtained more reliably. Therefore, the efficiency of thermoelectric conversion can be further improved.

In the thermoelectric conversion material, the structure of the thermoelectric conversion material may include an amorphous phase mainly composed of a base material element. The crystal phase composed of the matrix element may exist in the amorphous phase. The thermoelectric conversion material containing an amorphous phase can reduce thermal conductivity. Therefore, ZT can be increased. Moreover, the electrical conductivity of the thermoelectric conversion material can be improved by the presence of a crystal phase composed of a matrix element in the amorphous phase. Therefore, ZT can be increased. Therefore, the efficiency of thermoelectric conversion can be further improved.

In the thermoelectric conversion material, the first additive element may be a transition metal. By doing so, it becomes easy to form the first additional level having a small energy width. Therefore, the conductivity can be increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the second additional level includes an energy band closer to the first additional level of the valence band or the conduction band adjacent to the forbidden band of the base material and the first additional level. May exist between the two. By the second additional level, the Fermi level of the base material can be brought closer to the energy band closer to the first additional level of the valence band or the conduction band. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the state density of the first additional level may have a ratio of 0.1 or more with respect to the maximum value of the state density of the valence band adjacent to the forbidden band of the base material. By doing so, the state density of the first additional level can be made relatively large compared to the state density of the valence band. Therefore, the conductivity can be increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the content ratio of the first additive element may be not less than 0.1 at% and not more than 5 at%. By doing so, it becomes easy to form the first additional level having a small energy width. Therefore, the conductivity can be increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the base material may be a SiGe-based material. The ratio of the energy difference between the first additional level closest to the valence band of the base material and the valence band of the base material with respect to the band gap of the base material may be 20% or more. The ratio of the energy difference between the first additional level closest to the conduction band of the base material and the conduction band of the base material with respect to the band gap of the base material may be 20% or more. By including such a first additive element, it is possible to reliably form the first additional level as a new level within the forbidden band when the base material is a SiGe-based material. The SiGe-based material means a material in which at least part of Si and Ge in SiGe and SiGe is replaced with another element such as C, Sn, and the like. When there are a plurality of first additional levels, the first additional level closest to the valence band among the plurality of first additional levels and the valence band of the base material The energy difference ratio is 20% or more, and the energy difference ratio between the first additional level closest to the conduction band among the plurality of first addition levels and the conduction band of the base material May be 20% or more.

In the thermoelectric conversion material, the first additive element may be Au, Fe, Cu, Ni, Mn, Cr, V, Ti, Ag, Pd, Pt, or Ir. These elements are preferably used when the first additional level is formed in the forbidden band when the base material is a SiGe-based material.

In the thermoelectric conversion material, the first additive element may be Au or Cu. The second additive element may be B. Thus, when the base material is a SiGe-based material, a first additional level that becomes a new level in the forbidden band can be formed using Au or Cu as the first additive element. . Further, the Fermi level can be controlled by using B as the second additive element and forming an acceptor level by the second additional level formed by the second additive element. As a result, ZT can be increased more reliably and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the first additive element may be Fe. The second additive element may be P. Thus, when the base material is a SiGe-based material, it is possible to form a first additional level that becomes a new level in the forbidden band using Fe as a first additive element. Further, the Fermi level can be controlled by using P as the second additive element and forming a donor level by the second additional level formed by the second additive element. As a result, ZT can be increased more reliably and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the base material may be a MnSi-based material. The first additive element may be Re or W. The second additive element may be Cr or Fe. By doing in this way, electroconductivity can be raised more reliably. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved. The MnSi-based material means a material in which at least one part of Mn and Si in MnSi and MnSi is replaced with another element, for example, Al or W.

In the thermoelectric conversion material, the base material may be a SnSe-based material. The first additive element may be Sc, Ti, or Zr. The second additive element may be F, Cl, Br, I, N, P, As, Sb, Bi, B, Al, Ga, or In. By doing in this way, electroconductivity can be raised more reliably. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved. The SnSe-based material means a material in which at least part of Sn and Se in SnSe and SnSe is replaced with another element, for example, S or Te.

In the thermoelectric conversion material, the base material may be a Cu 2 _Se material. The first additive element may be V, Sc, Ti, Co, or Ni. The second additive element may be F, Cl, Br, I, N, P, As, Sb, Bi, Mg, Zn, or Cd. By doing in this way, electroconductivity can be raised more reliably. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved. The Cu ₂ Se material, _Cu 2 Se, and _Cu 2 In Se Cu and Se at least one of a part of another element, for example Ag, S, means a material which is replaced with Te.

The thermoelectric conversion element of the present application includes a thermoelectric conversion material portion, a first electrode disposed in contact with the thermoelectric conversion material portion, a second electrode disposed in contact with the thermoelectric conversion material portion and spaced apart from the first electrode, . The thermoelectric conversion material portion is made of the thermoelectric conversion material of the present application in which the component composition is adjusted so that the conductivity type is p-type or n-type.

The thermoelectric conversion element of the present application is made of a thermoelectric conversion material having an excellent thermoelectric conversion characteristic in which the component composition is adjusted so that the thermoelectric conversion material portion is p-type or n-type. Therefore, according to the thermoelectric conversion element of this application, the thermoelectric conversion element excellent in conversion efficiency can be provided.

The thermoelectric conversion module of the present application includes a plurality of the thermoelectric conversion elements. According to the thermoelectric conversion module of the present application, a thermoelectric conversion module with improved thermoelectric conversion efficiency can be obtained by including a plurality of thermoelectric conversion elements of the present application having excellent thermoelectric conversion efficiency.

The optical sensor of the present application includes an absorber that absorbs light energy and a thermoelectric conversion material portion connected to the absorber. The thermoelectric conversion material portion is made of the thermoelectric conversion material of the present application in which the component composition is adjusted so that the conductivity type is p-type or n-type.

The photosensor of the present application is made of a thermoelectric conversion material having an excellent thermoelectric conversion characteristic in which the composition of the thermoelectric conversion material portion is adjusted so that the conductivity type is p-type or n-type. Therefore, a highly sensitive optical sensor can be provided.

[Details of the embodiment of the present invention]
Next, an embodiment of the thermoelectric conversion material of the present application will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

(Embodiment 1)
The configuration of the thermoelectric conversion material according to Embodiment 1 of the present application will be described. The thermoelectric conversion material according to the first embodiment of the present application is a base material, which is a semiconductor composed of a base material element, and an element different from the base material element, and is a d-orbit or f located inside (outside) the outermost shell. A first additive element having an empty orbit in the orbit and a second additive element that is an element different from both the base material element and the first additive element. The difference between the number of electrons in the outermost shell of the second additive element and the number of electrons in the outermost shell of the base material element is 1. In the present embodiment, the base material is, for example, SiGe that is a semiconductor. Specifically, the base material elements are Si and Ge. The first additive element is Au. The second additive element is B. The first additional level formed by Au exists in the forbidden band of SiGe. The difference between the number of electrons in the outermost shell of B and the number of electrons in the outermost shells of Si and Ge, which are base materials, is 1.

Au is a transition metal. The first additional level formed by Au exists in the forbidden band of SiGe. The second additional level formed by B includes the valence band adjacent to the forbidden band of SiGe or the energy band closer to the first additional level of the conduction band and the first valence band and the first band. It exists between additional levels.

A method for manufacturing a thermoelectric conversion material according to Embodiment 1 of the present application will be briefly described. First, a sapphire substrate as a base substrate is prepared. Next, a plurality of raw material elements constituting the thermoelectric conversion material are vapor-deposited on the sapphire substrate by using, for example, an MBE (Molecular Beam Epitaxy) method using an evaporation apparatus. At this time, Si is simultaneously irradiated at a rate of 1 nm / min, Ge at 1 nm / min, Au at 0.1 nm / min, and B at a rate of 0.1 nm / min. By maintaining this state, an amorphous film having a total thickness of 200 nm or more is deposited and film formation is performed. The obtained product is annealed, specifically, for example, heated to 500 ° C. and held for 15 minutes. By this heat treatment, the first additive element Au and the second additive element B are activated. In this way, the thermoelectric conversion material according to Embodiment 1 is obtained.

FIG. 1 is a graph showing the relationship between the content ratio of Au and the value of ZT. FIG. 1 shows the relationship between the Au content and ZT when 3 at% B is added, and the relationship between the Au content and ZT when B is not added. In FIG. 1, the vertical axis indicates the value of ZT, and the horizontal axis indicates the content ratio (at%) of Au. In FIG. 1, the case where 3 at% of B which is the second additive element 10 is added and film formation is performed at an environmental temperature of 150 K is indicated by a circle. For reference, the case where B is 0 at%, that is, the case where film formation is performed at an environmental temperature of 150 K without adding the second additive element is also shown in FIG. The eye guide when B is added at 3 at% and the eye guide when the second additive element is not added are indicated by broken lines, respectively. About the thermoelectric characteristic, it measured with the thermoelectric characteristic measuring apparatus (RZ2001i by Ozawa Scientific Co., Ltd.). The measuring method of thermoelectric characteristics is as follows. First, the thermoelectric conversion material is fixed to a pair of quartz jigs so as to be bridged, and the atmosphere is heated in a resistance heating furnace. One side of the quartz jig is left hollow, and it is cooled by flowing nitrogen gas therein, and one end of the thermoelectric conversion material is cooled. Thereby, a temperature difference is provided to the thermoelectric conversion material. For the thermoelectric conversion material, a temperature difference between two points on the surface of the thermoelectric conversion material is measured using a platinum-platinum rhodium-based thermocouple (R thermocouple). By connecting a voltmeter to the thermocouple, the voltage generated by the temperature difference between the two points is measured. Thereby, it is possible to measure the generated voltage with respect to the temperature difference, and from this, it is possible to estimate the Seebeck coefficient of the material. Further, the resistance value is measured by a four-terminal method. That is, two electric wires are connected to the outside of the two platinum wires connected to the voltmeter. Current is passed through the wire, and the amount of voltage drop is measured with the inner voltmeter. In this way, the resistance value of the thermoelectric conversion material is measured by the four-terminal method.

Referring to FIG. 1, the case where the content ratio of B is 0 at%, that is, the case where the second additive element is not added will be described. As the content ratio of Au increases from 0 at%, the value of ZT gradually increases. ZT is about 0.6 at the maximum. At this time, the Au content is about 10 at%. When the Au content exceeds 10 at%, the value of ZT decreases. That is, when B is 0 at%, the content ratio of Au is 10 at% and ZT has a maximum value of 0.6.

FIG. 2 is a schematic diagram showing an energy state of a thermoelectric conversion material (SiGe) in the case of containing one additive element. That is, FIG. 2 shows the energy state of the thermoelectric conversion material that does not contain the second additive element defined in the thermoelectric conversion material of the present application. In FIG. 2, the vertical axis indicates the energy level, and the horizontal axis indicates the density of states. 2 shows the Fermi level E _F in broken lines. In FIG. 2, for example, Au is used as an additive element.

With reference to FIG. 2, a forbidden band 13 is formed between the valence band 11 and the conduction band 12. In the forbidden band 13, there is an additional level 14 formed by Au as an additive element. Energy width W ₁ is narrow in the state containing a small percentage of Au, the gap between the additional level 14 and the Fermi level E _F is generated. As you increase the content of Au as the attempt is made to increase in ZT, additional level 14 is in the vertical axis direction in the broad area of the conduction band 12 of the additional level 14 approaches to the Fermi level E _F . As a result, the value of ZT, as shown in FIG. 1 is slightly increased, but the energy width W ₁ of the additional level 14 becomes wider in the vertical axis direction. Such energy width W ₁ is wide additional level 14 can not increase the ZT efficiently.

Next, the case where the content ratio of B is 3 at% will be described. Referring to FIG. 1 again, when the B content ratio is 3 at%, the Au content ratio is 0.1 at% and ZT takes a value of about 1.0. When the content ratio of Au is 1 at%, the value of ZT exceeds 1.0. Specifically, the value of ZT is 1.2 to 1.3. And when the content rate of Au is 5.4 at%, the value of ZT may have risen to about 1.4. When the content ratio of Au is 8.9 at%, the value of ZT is less than 1.0. These compositions can be measured by a general composition analysis method. Examples thereof include an electron beam microanalyzer method and energy dispersive X-ray spectroscopy.

FIG. 3 is a schematic diagram showing the energy state of the thermoelectric conversion material containing the first additive element and the second additive element. In FIG. 3, the vertical axis indicates the energy level, and the horizontal axis indicates the density of states. Also in FIG. 3 shows the Fermi level E _F in broken lines.

With reference to FIG. 3, in the thermoelectric conversion material according to Embodiment 1 of the present application, a forbidden band 13 exists between the valence band 11 and the conduction band 12. The first additional level 15 and the second additional level 16 exist in the forbidden band 13. The first additional level 15 is formed of Au as the first additive element. Energy width W ₂ of the first additional level 15 in this case, since the content ratio of Au is smaller, narrower than the energy width W ₁ of the additional level 14 shown in FIG.

The second additional level 16 is formed by B which is the second additive element. The difference between the number of electrons of B and the base material elements Si and Ge is 1. The second additional level 16 formed by B is a valence electron that is an energy band closer to the first additional level 15 of the valence band 11 or the conduction band 12 adjacent to the forbidden band 13 of SiGe. It exists between the band 11 and the first additional level 15. In the present embodiment, an acceptor level can be formed by the second additional level 16.

Since the thermoelectric conversion material according to Embodiment 1 includes SiGe as a base material, the Seebeck coefficient can be increased. As a result, the dimensionless figure of merit ZT can be increased by employing SiGe as the base material.

Since the thermoelectric conversion material according to Embodiment 1 includes Au as the first additive element, the first additional level can be formed as a new level. Au is because it has an empty orbital to d orbital located inside the P shell, it is possible to reduce the energy width W ₂ of the first additional level. Therefore, the conductivity can be increased despite the high Seebeck coefficient. The thermoelectric conversion material according to the first embodiment includes B which is an element different from both of the base elements Si and Ge and the first additive element Au, and the number of electrons in the outermost shell of B and the base material The difference from the number of electrons in the outermost shell of the elements Si and Ge is 1. Therefore, it is possible to control the Fermi level by forming an acceptor level by the second additional level 16 formed by B. As a result, ZT can be increased more reliably and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material according to Embodiment 1, Au, which is a transition metal, is applied as the first additive element. By doing so, it becomes easy to form the first additional level 15 having a small energy width. Therefore, the conductivity can be increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material according to Embodiment 1, the first additional level 15 formed of Au exists in the forbidden band 13 of SiGe. The second additional level 16 formed by B is a valence electron that is an energy band closer to the first additional level 15 of the valence band 11 or the conduction band 12 adjacent to the forbidden band 13 of SiGe. It exists between the band 11 and the first additional level 15. Since the first additional level 15 exists in the forbidden band 13, a new level based on the first additional level 15 can be formed in the forbidden band 13. The second additional level 16 formed by B is a valence band 11 which is an energy band of the SiGe Fermi level closer to the first additional level 15 of the valence band 11 or the conduction band 12. Can be approached. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material according to the first embodiment, the state density of the first additional level 15 formed of Au is 0 with respect to the maximum value of the state density of the valence band 11 adjacent to the forbidden band 13 of SiGe. Has a ratio of 1 or more (see FIG. 3). By doing so, the state density of the first additional level 15 can be made relatively large compared to the state density of the valence band 11. Therefore, the conductivity can be increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material according to Embodiment 1, the content ratio of Au may be 0.1 at% or more and 5 at% or less. By doing so, it becomes easy to form the first additional level 15 having a small energy width. Therefore, the conductivity can be increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved. The same applies to thermoelectric conversion materials according to Embodiment 2 below.

In the above embodiment, the base material is a semiconductor made of SiGe, the first additive element is Au, and the second additive element is B. However, the thermoelectric conversion material of the present application is not limited to this. Absent. For example, the base material may be a SiGe-based material. The ratio of the energy difference between the first additional level closest to the valence band of the base material and the valence band of the base material with respect to the band gap of the base material may be 20% or more. The ratio of the energy difference between the first additional level closest to the conduction band of the base material and the conduction band of the base material with respect to the band gap of the base material may be 20% or more. By including such a first additive element, it is possible to reliably form the first additional level as a new level within the forbidden band when the base material is a SiGe-based material. The SiGe-based material means a material in which at least part of Si and Ge in SiGe and SiGe is replaced with another element such as C, Sn, and the like.

FIG. 4 is a diagram showing energy levels formed by each element as the first additive element when the base material is SiGe. In FIG. 4, a conduction band is shown in a region 46a, and a valence band is shown in a region 46b. As shown in FIG. 4, when the first additive element is Fe in FIG. 4, the band gap is the difference between the energy closest to the region 46b in the region 46a and the energy closest to the region 46a in the region 46b. Indicated by L. The first additional level is indicated by an energy level 47 between the region 46a and the region 46b, for example, as shown when the element is Cu. FIG. 4 is derived based on the first principle calculation. In FIG. 4, as for the first additional level, some energy levels are expressed by a single line such as Cu, and some energy levels are expressed by two lines such as Fe. In addition, depending on the element, the energy level may be represented by three or more lines. Thus, when there are a plurality of first additional levels, the first additional level located closest to the valence band among the plurality of first additional levels and the valence band of the base material The difference in energy between the first additional level at the position closest to the conduction band and the conduction band of the base material among the plurality of first additional levels is 20% or more. The ratio may be 20% or more.

Referring to FIG. 4, when SiGe is used as the base material, the first additional level is the first additional level and the base that are closest to the valence band of the base material with respect to the band gap of the base material. The ratio of the energy difference from the valence band of the material is 20% or more, and the first additional level located closest to the conduction band of the base material and the conduction band of the base material with respect to the band gap of the base material Examples of elements having an energy difference ratio of 20% or more include Au, Fe, Cu, Ni, Mn, Cr, V, Ti, Ag, Pd, Pt, and Ir. That is, when SiGe is used as the base material, the first additive element may be Au, Fe, Cu, Ni, Mn, Cr, V, Ti, Ag, Pd, Pt, or Ir.

Specifically, for example, the first additive element is Au or Cu, and the second additive element is B. The first additional level formed by Au or Cu exists in the forbidden band of SiGe. The second additional level formed by B includes the valence band adjacent to the forbidden band of SiGe or the energy band closer to the first additional level of the conduction band and the first valence band and the first band. It exists between additional levels. Thus, when the base material is SiGe, the first additional level that becomes a new level in the forbidden band can be formed using Au or Cu as the first additive element. Further, the Fermi level can be controlled by using B as the second additive element and forming an acceptor level by the second additional level formed by the second additive element. As a result, ZT can be increased more reliably and the efficiency of thermoelectric conversion can be improved.

(Embodiment 2)
In the thermoelectric conversion material according to Embodiment 2, in the thermoelectric conversion material of Embodiment 1 described above, the first additive element is Fe, and the second additive element is P. The first additional level formed by Fe exists in the forbidden band of SiGe. The second additional level formed by P includes the conduction band and the first addition which are energy bands closer to the first additional level of the valence band or the conduction band adjacent to the forbidden band of SiGe. It exists between the levels. By doing so, when the base material is SiGe, the first additional level that becomes a new level in the forbidden band can be formed using Fe as the first additive element. Further, the Fermi level can be controlled by using P as the second additive element and forming a donor level by the second additional level formed by the second additive element. As a result, ZT can be increased more reliably and the efficiency of thermoelectric conversion can be improved.

The thermoelectric conversion material according to Embodiment 2 can be manufactured by the following manufacturing method. First, the weighed Si, Ge, Fe and P powders are placed in a stainless steel pot. In this case, the content ratio of each element is adjusted to be Si ₆₃ Ge ₂₄ P ₁₀ Fe ₃ . Further, the inside of the pot is filled with a forming gas which is a mixed gas of hydrogen and nitrogen having a hydrogen content of 4% by volume or less to form a reducing atmosphere. Then, an amorphous powder obtained by adding Fe and P powder to SiGe is obtained by mechanical alloying. That is, the mechanical alloying is performed in a mixed gas of hydrogen and nitrogen having a hydrogen content of 4% by volume or less. In this way, mechanical alloying is performed in a reducing atmosphere to obtain an amorphous semiconductor material powder.

Next, in a state where the inside of the glove box is in an atmosphere of nitrogen gas, the obtained powder is filled into a die, and a sintered body is formed by a spark plasma sintering method. The temperature at this time can be set to 600 ° C., for example. In this manner, a thermoelectric conversion material made of a sintered body in which the crystal phase of the base material element in the amorphous phase, that is, the SiGe crystal phase in the present embodiment, is manufactured.

FIG. 5 is a schematic view showing the state of the structure of the thermoelectric conversion material in the second embodiment. Referring to FIG. 5, the structure of thermoelectric conversion material 1 includes an amorphous phase 2 and a crystal phase 3. The amorphous phase 2 is mainly composed of SiGe which is a base material element. Here, the content ratio of SiGe contained as a main component is, for example, 50% by mass or more, preferably 90% by mass or more, and more preferably 95% or more. The crystal phase 3 is a microcrystal made of SiGe which is a base material element. Crystal phase 3 exists in amorphous phase 2. In the present embodiment, a plurality of granular crystal phases 3 are dispersed in the amorphous phase 2. The grain size of the crystal phase 3 is 50 nm or less. The measurement of the grain size of the crystal phase 3 can be calculated from the half width of the peak indicating SiGe in the X-ray diffraction pattern shown in FIG. In addition, the thermoelectric conversion material in Embodiment 1 mentioned above also has the same structure. The same applies to the following embodiments.

In the thermoelectric conversion material 1, the structure of the thermoelectric conversion material includes an amorphous phase 2 mainly composed of a base material element, and the crystal phase 3 of the base material element exists in the amorphous phase 2. The thermoelectric conversion material containing the amorphous phase 2 can reduce the thermal conductivity. Therefore, ZT can be increased. Further, the presence of the crystal phase 3 made of the base material element in the amorphous phase 2 can improve the conductivity of the thermoelectric conversion material 1. Therefore, ZT can be increased. Therefore, the efficiency of thermoelectric conversion can be further improved. Further, since the crystal phase 3 has higher conductivity than the amorphous phase 2, ZT increases. On the other hand, when the grain size of the crystal phase 3 becomes too large, the thermal conductivity tends to increase. An increase in thermal conductivity can be suppressed by setting the grain size of the crystal phase 3 made of the base material element to 50 nm or less. Therefore, according to such a thermoelectric conversion material 1, an increase in thermal conductivity can be suppressed while improving electrical conductivity. Therefore, the efficiency of thermoelectric conversion can be further improved by increasing ZT.

The relationship between the temperature of the obtained thermoelectric conversion material and ZT was derived. FIG. 6 is a graph showing the relationship between the temperature of the thermoelectric conversion material and ZT in the second embodiment. In FIG. 6, the horizontal axis indicates temperature (° C.), and the vertical axis indicates ZT. The eye guide for the plot of the graph is indicated by line 5 in FIG. FIG. 6 shows the case of the thermoelectric conversion material in Embodiment 2 in which mechanical alloying is performed for 10 hours. ZT in FIG. 6 measured the resistivity, Seebeck coefficient and thermal conductivity of the thermoelectric conversion material in vacuum, and derived the value of ZT from the obtained measurement results. Moreover, FIG. 6 shows the result at the time of measuring when heating from low temperature to high temperature.

Referring to FIG. 6, the value of ZT increases with increasing temperature from room temperature to 700 ° C. At 700 ° C., the value of ZT is 3 or more, which is a very high value. When it exceeds 700 ° C., ZT gradually decreases. Therefore, for example, thermoelectric conversion can be performed with a high ZT value by use within a range not exceeding 700 ° C. or use near 700 ° C., and the efficiency of thermoelectric conversion can be further improved.

FIG. 7 is an X-ray diffraction pattern of the thermoelectric conversion material in the second embodiment. In FIG. 7, an X-ray diffraction pattern 6a and an X-ray diffraction pattern 6b are shown when measured at 900 ° C. The sample which measured thermal conductivity with X-ray diffraction pattern 6a is shown, and the sample which measured resistivity with X-ray diffraction pattern 6b is shown. The case of sintering at 600 ° C. with the X-ray diffraction pattern 6c is shown. An X-ray diffraction pattern when no spark plasma sintering is performed is shown by a line 6d.

For measurement of the X-ray diffraction pattern, D8 Advance manufactured by Bruker was used as the X-ray diffractometer. CuKα ray was used as the X-ray source, and the θ-2θ method (Bragg Brentano type divergent condensing system) was used as the measurement method. For Rietveld analysis described later, PROGRAM FullProf. Analysis was performed using 2k.

Referring to FIG. 7, the peak _{A 1} is a peak corresponding to the crystalline phases of SiGe. In the case of the X-ray diffraction pattern 6a measured at 900 ° C., a peak showing a crystal phase of SiGe, which is a crystal phase composed of a base material element, appears. When derived from the half-value width of the peak of the crystal phase made of SiGe shown in the X-ray diffraction pattern 6a, the grain size of the crystal phase made of SiGe is 50 nm. The peak A ₁ is a peak having the maximum intensity among the peaks indicating the SiGe crystal phase.

Further, the peak A ₂ is a peak corresponding to the crystalline phase of Fe. In the X-ray diffraction pattern 6a, a peak indicating a crystal phase of Fe that is a crystal phase containing the first additive element appears. The peak A ₂ is the peak having the maximum intensity among peaks indicating a crystal phase of Fe. The ratio of the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase of Fe to the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase made of SiGe is 1.6%. That is, the ratio of the intensity of the peak having the maximum intensity among the peaks showing the Fe crystal phase to the intensity of the peak having the maximum intensity among the peaks showing the crystal phase made of SiGe is 2.0% or less.

Moreover, the peak A ₃ is a peak indicating a crystal phase of P ₄ Si ₄ . In the X-ray diffraction pattern 6a, a peak indicating a crystal phase of P ₄ Si ₄ that is a crystal phase containing the second additive element appears. This peak A ₃ is a peak having the maximum intensity among the peaks showing the crystal phase of P ₄ Si ₄ . The ratio of the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase of P ₄ Si ₄ to the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase made of SiGe is also 1.6%. . That is, the ratio of the peak intensity having the maximum intensity among the peaks showing the crystal phase of P ₄ Si _{4 to} the peak intensity having the maximum intensity among the peaks showing the crystal phase made of SiGe is 2.0% or less. .

In the case of the X-ray diffraction pattern 6b measured at 900 ° C., a peak showing a crystal phase of SiGe which is a crystal phase composed of a base material element appears. When derived from the half width of the peak of the crystal phase made of SiGe shown in the X-ray diffraction pattern 6b, the grain size of the crystal phase made of SiGe is 50 nm. The peak A ₁ is a peak having the maximum intensity among the peaks showing a crystal phase made of SiGe. In the X-ray diffraction pattern 6b, a peak indicating a crystal phase of Fe that is a crystal phase containing the first additive element appears. The peak A ₂ is the peak having the maximum intensity among peaks indicating a crystal phase of Fe. The ratio of the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase of Fe to the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase made of SiGe is 1.6%. That is, the ratio of the intensity of the peak having the maximum intensity among the peaks showing the Fe crystal phase to the intensity of the peak having the maximum intensity among the peaks showing the crystal phase made of SiGe is 2.0% or less. In the X-ray diffraction pattern 6b, no peak indicating the crystal phase of P ₄ Si ₄ appears. That is, the ratio of the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase of P ₄ Si ₄ to the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase made of SiGe is 2.0% or less. It is.

In the case of the X-ray diffraction pattern 6c sintered at 600 ° C., a peak indicating a SiGe crystal phase, which is a crystal phase composed of a base material element, appears. When derived from the half width of the peak of the crystal phase made of SiGe shown in the X-ray diffraction pattern 6c, the grain size of the crystal phase made of SiGe is 16 nm. In the X-ray diffraction pattern 6c, the peak indicating the Fe crystal phase and the peak indicating the P ₄ Si ₄ crystal phase do not appear. That is, the ratio of the intensity of the peak having the maximum intensity among the peaks showing the Fe crystal phase to the intensity of the peak having the maximum intensity among the peaks showing the crystal phase made of SiGe is 2.0% or less. The ratio of the intensity of the peak having the maximum intensity among the peaks showing the crystal phase of P ₄ Si ₄ to the intensity of the peak having the maximum intensity among the peaks showing the crystal phase made of SiGe is 2.0% or less. It is. That is, the peak indicating the crystal phase including at least one of the first additive element and the second additive element with respect to the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase composed of the matrix element. The ratio of the peak intensity having the maximum intensity is 2.0% or less.

Even when the spark plasma sintering indicated by the X-ray diffraction pattern 6d is not performed, a peak showing a crystal phase made of SiGe, which is a crystal phase made of a base material element, appears. Derived from the half width of the peak of the crystal phase made of SiGe shown in the X-ray diffraction pattern 6d, the grain size of the crystal phase of SiGe is 10 nm. In the X-ray diffraction pattern 6d, neither a peak indicating the Fe crystal phase nor a peak indicating the P ₄ Si ₄ crystal phase appears.

In the X-ray diffraction pattern of the thermoelectric conversion material, Fe as the first additive element and second additive element with respect to the intensity of the peak having the maximum intensity among the peaks showing the crystal phase composed of SiGe as the base material element The ratio of the intensity of the peak having the maximum intensity among the peaks showing the crystal phase containing at least one of P is 2.0% or less. In the thermoelectric conversion material, when a large amount of the crystal phase containing at least one of the first additive element and the second additive element is precipitated, the carrier concentration is reduced compared to the case where the crystal phase is small, and the Fermi level is reduced. The position of the position is shifted or the density of the first additional level is lowered. The effect of forming the first additional level and the effect of forming the second additional level are difficult to obtain due to at least one of these factors or both factors. According to the thermoelectric conversion material, since the precipitation amount of the first additive element as a crystal phase and the precipitation amount of the second additive element as a crystal phase is small, the formation of the first additional level by the first additive element The effect and the effect of forming the second additional level by the second additive element can be obtained more reliably. Therefore, the efficiency of thermoelectric conversion can be further improved.

In addition, in the X-ray diffraction pattern shown in FIG. 7, a Rietveld analysis is performed for the case where measurement is performed at 900 ° C. indicated by the X-ray diffraction pattern 6a, and at least one of the first additive element and the second additive element The proportion of the crystal phase containing one was derived. In this case, a ratio of both the Fe crystal phase that is the crystal phase containing the first additive element and the P ₄ Si ₄ crystal phase that is the crystal phase containing the second additive element was derived. In the thermoelectric conversion material, a crystal phase including at least one of the first additive element and the second additive element with respect to the entire structure of the thermoelectric conversion material, in this case, a crystal phase of Fe and a crystal of P ₄ Si ₄ The ratio of both phases was 6.0% by volume or less, specifically 5.6% by volume. When sintered at 600 ° C. indicated by the X-ray diffraction pattern 6c, the ratio of the crystal phase containing at least one of the first additive element and the second additive element to the entire thermoelectric conversion material is 0% by volume. Met. That is, the crystal phase containing at least one of the first additive element and the second additive element with respect to the entire structure of the thermoelectric conversion material is 6.0% by volume or less.

Since such a thermoelectric conversion material has a small amount of precipitation as a crystal phase of the first additive element and a crystal phase of the second additive element, formation of the first additional level by the first additive element And the effect of forming the second additional level by the second additive element can be obtained more reliably. Therefore, the efficiency of thermoelectric conversion can be further improved.

In the above embodiment, the thermoelectric conversion material of the present application may include the first additive element having an empty orbit in the f orbit located inside the outermost shell. The same applies to the following embodiments.

(Embodiment 3)
In the thermoelectric conversion material according to the present embodiment, the base material is a MnSi-based material, the first additive element is Re or W, and the second additive element is Cr or Fe. With the thermoelectric conversion material according to the second embodiment, the conductivity can be more reliably increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

The thermoelectric conversion material according to Embodiment 3 may be manufactured by the following manufacturing method. First, using a high-frequency heating furnace, a raw material in which base materials Mn and Si, a first additive element Re, and a second additive element Cr are mixed is melted and hardened, Make an alloy. The produced mother alloy is melted and sprayed onto a rotating copper roll. By performing such a liquid quenching method in a non-equilibrium state, a ribbon-like (flaky) amorphous alloy is obtained. The obtained amorphous alloy is subjected to a heat treatment by a spark plasma sintering method to obtain a thermoelectric conversion material that is a bulk-shaped formed body. In this manner, the thermoelectric conversion material according to Embodiment 2 may be obtained.

8 and 9 are graphs showing the density of states when the content ratio of Re added as the first additive element to MnSi is changed. FIG. 8 shows a case of actual measurement by HAXPES (Hard X-ray Photoelectron Spectroscopy), and FIG. 9 shows a case based on theoretical calculation. 8 and 9, a line 17a indicates a case where Re is not added, a line 17b indicates a case where Re is added at 4 at%, and a line 17c indicates a case where Re is added at 6 at%. 8 and 9, the horizontal axis represents energy, and the vertical axis in FIG. 8 represents intensity normalized with a value of 10 to 15 eV. The vertical axis in FIG. 9 indicates the spectral conductivity.

8 and 9, it can be understood that a peak of a new level appears due to the addition of Re at the position of the end of the valence band adjacent to the forbidden band indicated by the arrow. By adding Re, the first added level having a small and narrow energy width can be formed.

(Embodiment 4)
In the thermoelectric conversion material according to the present embodiment, the base material is a SnSe-based material, the first additive element is Sc, Ti, or Zr, and the second additive element is F, Cl, Br, I , N, P, As, Sb, Bi, B, Al, Ga, or In. With the thermoelectric conversion material according to Embodiment 3, the conductivity can be more reliably increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

FIG. 10 is a diagram showing an example of a band structure in the case where the first added level of Sc as the first additive element exists in the SnSe-based material. In FIG. 10, the SnSe band is calculated by the FLAPW (Full-potential Linearized Augmented Plane Wave) method. The exchange interaction is handled within the framework of the GGA (Generalized Gradient Application) method. The band of the 3d orbit of Sc is derived by cluster calculation (referred to as calculation by a cluster model). FIG. 11 is a diagram illustrating an example of a band structure in the case where the first added level of Ti and Zr as the first additive element exists in the SnSe-based material. Also in FIG. 11, the FLAPW method and the GGA method are used. Further, the band of 3d orbital of Ti and the band of 4d orbital of Zr are also derived by cluster calculation.

Referring to FIGS. 10 and 11, in the vicinity of the end of the conduction band adjacent to the forbidden band of the SnSe band, the first additive elements Sc, Ti, and Zr have a small energy width and a steep first. Can be formed.

(Embodiment 5)
In the thermoelectric conversion material according to the present embodiment, the base material is a Cu ₂ Se-based material, the first additive element is V, Sc, Ti, Co, or Ni, and the second additive element is F , Cl, Br, I, N, P, As, Sb, Bi, Mg, Zn or Cd. With the thermoelectric conversion material according to the fourth embodiment, the conductivity can be more reliably increased. As a result, ZT can be increased and the efficiency of thermoelectric conversion can be improved.

FIG. 12 is a diagram illustrating an example of a band structure in the case where the first additional level of Sc, Ti, and V as the first additive element exists in the Cu ₂ Se-based material. Also in FIG. 12, the Cu ₂ Se band is calculated by the FLAPW method. The exchange interaction is also handled within the framework of the GGA method. The 3d orbital band of Sc, the 3d orbital band of Ti, and the 3d orbital band of V are each derived by cluster calculation. FIG. 13 is a diagram illustrating an example of a band structure in the case where the first added level of Co and Ni as the first additive element exists in the SnSe-based material. Also in FIG. 13, the FLAPW method and the GGA method are used. The 3d orbital band of Co and the 3d orbital band of Ni are also derived by cluster calculation. In FIG. 12 and FIG. 13, “× 8” in the annotation indicates that the signal is displayed with a magnification of 8 times.

Referring to FIGS. 12 and 13, in the vicinity of the end of the conduction band or valence band adjacent to the forbidden band of the Cu ₂ Se band, Sc, Ti, V, Co, Ni, which are the first additive elements Can form a steep band with a small energy width.

(Embodiment 6)
Next, a power generation element will be described as an embodiment of a thermoelectric conversion element using the thermoelectric conversion material according to the present application.

FIG. 14 is a schematic diagram showing the structure of a π-type thermoelectric conversion element (power generation element) 21 that is a thermoelectric conversion element in the present embodiment. Referring to FIG. 14, a π-type thermoelectric conversion element 21 includes a p-type thermoelectric conversion material portion 22 that is a first thermoelectric conversion material portion, an n-type thermoelectric conversion material portion 23 that is a second thermoelectric conversion material portion, and a high temperature. A side electrode 24, a first low temperature side electrode 25, a second low temperature side electrode 26, and a wiring 27 are provided.

The p-type thermoelectric conversion material part 22 is made of the thermoelectric conversion material of Embodiment 1 in which the component composition is adjusted so that, for example, the conductivity type is p-type. The p-type thermoelectric conversion material is formed by doping the thermoelectric conversion material of Embodiment 1 constituting the p-type thermoelectric conversion material portion 22 with, for example, a p-type impurity that generates p-type carriers (holes) that are majority carriers. The conductivity type of the portion 22 is p-type.

The n-type thermoelectric conversion material portion 23 is made of the thermoelectric conversion material of Embodiment 1 in which the component composition is adjusted so that the conductivity type is n-type, for example. The n-type thermoelectric conversion material portion is formed by doping the thermoelectric conversion material of the first embodiment constituting the n-type thermoelectric conversion material portion 23 with, for example, an n-type impurity that generates n-type carriers (electrons) that are majority carriers. The conductivity type 23 is n-type.

The p-type thermoelectric conversion material part 22 and the n-type thermoelectric conversion material part 23 are arranged side by side at intervals. The high temperature side electrode 24 is disposed so as to extend from one end portion 31 of the p-type thermoelectric conversion material portion 22 to one end portion 32 of the n-type thermoelectric conversion material portion 23. The high temperature side electrode 24 is disposed so as to contact both one end portion 31 of the p-type thermoelectric conversion material portion 22 and one end portion 32 of the n-type thermoelectric conversion material portion 23. The high temperature side electrode 24 is disposed so as to connect one end 31 of the p-type thermoelectric conversion material part 22 and one end 32 of the n-type thermoelectric conversion material part 23. The high temperature side electrode 24 is made of a conductive material, for example, a metal. The high temperature side electrode 24 is in ohmic contact with the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23.

The first low temperature side electrode 25 is disposed in contact with the other end 33 of the p-type thermoelectric conversion material portion 22. The first low temperature side electrode 25 is disposed away from the high temperature side electrode 24. The first low temperature side electrode 25 is made of a conductive material, for example, a metal. The first low temperature side electrode 25 is in ohmic contact with the p-type thermoelectric conversion material part 22.

The second low temperature side electrode 26 is disposed in contact with the other end 34 of the n-type thermoelectric conversion material portion 23. The second low temperature side electrode 26 is disposed apart from the high temperature side electrode 24 and the first low temperature side electrode 25. The second low temperature side electrode 26 is made of a conductive material, for example, a metal. The second low temperature side electrode 26 is in ohmic contact with the n-type thermoelectric conversion material portion 23.

The wiring 27 is made of a conductor such as metal. The wiring 27 electrically connects the first low temperature side electrode 25 and the second low temperature side electrode 26.

In the π-type thermoelectric conversion element 21, for example, one end portion 31 of the p-type thermoelectric conversion material portion 22 and one end portion 32 side of the n-type thermoelectric conversion material portion 23 are at a high temperature. When the temperature difference is formed so that the end 33 and the other end 34 side of the n-type thermoelectric conversion material portion 23 are at a low temperature, in the p-type thermoelectric conversion material portion 22, from one end portion 31 side. P-type carriers (holes) move toward the other end 33 side. At this time, in the n-type thermoelectric conversion material portion 23, n-type carriers (electrons) move from one end portion 32 side toward the other end portion 34 side. As a result, a current flows through the wiring 27 in the direction of arrow I. In this way, in the π-type thermoelectric conversion element 21, power generation by thermoelectric conversion using a temperature difference is achieved. That is, the π-type thermoelectric conversion element 21 is a power generation element.

As the material constituting the p-type thermoelectric conversion material part 22 and the n-type thermoelectric conversion material part 23, for example, the thermoelectric conversion material of Embodiment 1 in which the value of ZT is increased is employed. As a result, the π-type thermoelectric conversion element 21 is a highly efficient power generation element.

In the above embodiment, the π-type thermoelectric conversion element has been described as an example of the thermoelectric conversion element of the present application, but the thermoelectric conversion element of the present application is not limited thereto. The thermoelectric conversion element of the present application may be a thermoelectric conversion element having another structure such as an I-type (unileg type) thermoelectric conversion element.

(Embodiment 7)
A power generation module as a thermoelectric conversion module can be obtained by electrically connecting a plurality of π-type thermoelectric conversion elements 21. The power generation module 41 that is the thermoelectric conversion module of the present embodiment has a structure in which a plurality of π-type thermoelectric conversion elements 21 are connected in series.

FIG. 15 is a diagram showing an example of the structure of the power generation module. Referring to FIG. 15, the power generation module 41 of the present embodiment corresponds to the p-type thermoelectric conversion material part 22, the n-type thermoelectric conversion material part 23, the first low-temperature side electrode 25, and the second low-temperature side electrode 26. Low

temperature side electrodes

25, 26, a high temperature side electrode 24, a low temperature side insulator substrate 28, and a high temperature side insulator substrate 29. The low temperature side insulator substrate 28 and the high temperature side insulator substrate 29 are made of ceramic such as alumina. The p-type thermoelectric conversion material portions 22 and the n-type thermoelectric conversion material portions 23 are alternately arranged. The low

temperature side electrodes

25 and 26 are disposed in contact with the p-type thermoelectric conversion material part 22 and the n-type thermoelectric conversion material part 23 in the same manner as the π-type thermoelectric conversion element 21 described above. The high temperature side electrode 24 is disposed in contact with the p-type thermoelectric conversion material part 22 and the n-type thermoelectric conversion material part 23 in the same manner as the π-type thermoelectric conversion element 21 described above. The p-type thermoelectric conversion material part 22 is connected to the n-type thermoelectric conversion material part 23 adjacent to one side by a common high-temperature side electrode 24. The p-type thermoelectric conversion material part 22 is connected to the n-type thermoelectric conversion material part 23 adjacent to the side different from the one side by common low-

temperature side electrodes

25 and 26. In this way, all the p-type thermoelectric conversion material portions 22 and the n-type thermoelectric conversion material portions 23 are connected in series.

The low temperature side insulator substrate 28 is arranged on the main surface side opposite to the side in contact with the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23 of the low

temperature side electrodes

25 and 26 having a plate shape. Is done. One low temperature side insulator substrate 28 is disposed for a plurality of (all) low

temperature side electrodes

25, 26. The high temperature side insulator substrate 29 is disposed on the opposite side to the side in contact with the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23 of the high temperature side electrode 24 having a plate shape. One high temperature side insulator substrate 29 is arranged for a plurality of (all) high temperature side electrodes 24.

Of the p-type thermoelectric conversion material part 22 and the n-type thermoelectric conversion material part 23 connected in series, the p-type thermoelectric conversion material part 22 or the n-type thermoelectric conversion material part 23 positioned at both ends, or the low-temperature side electrode 24 A wiring 27 is connected to the

side electrodes

25 and 26. When the temperature difference is formed so that the high temperature side insulator substrate 29 side is at a high temperature and the low temperature side insulator substrate 28 side is at a low temperature, the p-type thermoelectric conversion material part 22 and the n-type thermoelectric conversion material part connected in series 23, a current flows in the direction of arrow I as in the case of the π-type thermoelectric conversion element 21. In this way, in the power generation module 41, power generation by thermoelectric conversion using a temperature difference is achieved.

(Embodiment 8)
Next, an infrared sensor that is an optical sensor will be described as another embodiment of the thermoelectric conversion element using the thermoelectric conversion material according to the present application.

FIG. 16 is a diagram illustrating an example of the structure of the infrared sensor 51. Referring to FIG. 16, infrared sensor 51 includes a p-type thermoelectric conversion material portion 52 and an n-type thermoelectric conversion material portion 53 that are arranged adjacent to each other. The p-type thermoelectric conversion material part 52 and the n-type thermoelectric conversion material part 53 are formed on the substrate 54.

The infrared sensor 51 includes a substrate 54, an etching stop layer 55, an n-type thermoelectric conversion material layer 56, an n ⁺ -type ohmic contact layer 57, an insulator layer 58, a p-type thermoelectric conversion material layer 59, and an n side. An ohmic contact electrode 61, a p-side ohmic contact electrode 62, a heat absorption pad 63, an absorber 64, and a protective film 65 are provided.

The substrate 54 is made of an insulator such as silicon dioxide. A concave portion 66 is formed in the substrate 54. The etching stop layer 55 is formed so as to cover the surface of the substrate 54. The etching stop layer 55 is made of an insulator such as silicon nitride. A gap is formed between the etching stop layer 55 and the recess 66 of the substrate 54.

The n-type thermoelectric conversion material layer 56 is formed on the main surface of the etching stop layer 55 opposite to the substrate 54. The n-type thermoelectric conversion material layer 56 is made of, for example, the thermoelectric conversion material of Embodiment 1 in which the component composition is adjusted so that the conductivity type is n-type. The n-type thermoelectric conversion material layer 56 is doped with, for example, an n-type impurity that generates n-type carriers (electrons), which are majority carriers, in the thermoelectric conversion material of the first embodiment constituting the n-type thermoelectric conversion material layer 56. The conductivity type 56 is n-type. The n ⁺ -type ohmic contact layer 57 is formed on the main surface of the n-type thermoelectric conversion material layer 56 opposite to the etching stop layer 55. In the n ⁺ -type ohmic contact layer 57, for example, an n-type impurity that generates n-type carriers (electrons) that are majority carriers is doped at a higher concentration than the n-type thermoelectric conversion material layer 56. Thereby, the conductivity type of the n ⁺ -type ohmic contact layer 57 is n-type.

The n-side ohmic contact electrode 61 is disposed so as to be in contact with the central portion of the main surface of the n ⁺ -type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56. The n-side ohmic contact electrode 61 is made of a material that can make ohmic contact with the n ⁺ -type ohmic contact layer 57, for example, a metal. An insulator layer 58 made of an insulator such as silicon dioxide is disposed on the main surface of the n ⁺ -type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56. The insulator layer 58 is disposed on the main surface of the n ⁺ -type ohmic contact layer 57 on the p-type thermoelectric conversion material part 52 side when viewed from the n-side ohmic contact electrode 61.

A protective film 65 is further disposed on the main surface of the n ⁺ -type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56. The protective film 65 is disposed on the main surface of the n ⁺ -type ohmic contact layer 57 on the side opposite to the p-type thermoelectric conversion material part 52 when viewed from the n-side ohmic contact electrode 61. On the main surface of the n ⁺ -type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56, another n-side ohmic contact is provided on the opposite side of the n-side ohmic contact electrode 61 with the protective film 65 interposed therebetween. Contact electrode 61 is disposed.

A p-type thermoelectric conversion material layer 59 is disposed on the main surface of the insulator layer 58 opposite to the n ⁺ -type ohmic contact layer 57. The p-type thermoelectric conversion material layer 59 is made of, for example, the thermoelectric conversion material of Embodiment 1 in which the component composition is adjusted so that the conductivity type is p-type. The p-type thermoelectric conversion material is formed by doping the thermoelectric conversion material of the first embodiment constituting the p-type thermoelectric conversion material layer 59 with, for example, a p-type impurity that generates p-type carriers (holes) that are majority carriers. The conductivity type of the layer 59 is p-type.

A protective film 65 is disposed at the center of the main surface of the p-type thermoelectric conversion material layer 59 opposite to the insulator layer 58. A pair of p-side ohmic contact electrodes 62 sandwiching the protective film 65 are disposed on the main surface of the p-type thermoelectric conversion material layer 59 opposite to the insulator layer 58. The p-side ohmic contact electrode 62 is made of a material that can make ohmic contact with the p-type thermoelectric conversion material layer 59, for example, a metal. Of the pair of p-side ohmic contact electrodes 62, the p-side ohmic contact electrode 62 on the n-type thermoelectric conversion material part 53 side is connected to the n-side ohmic contact electrode 61.

Absorber 64 is arranged so as to cover the main surface of p-side ohmic contact electrode 62 and n-side ohmic contact electrode 61 connected to each other on the side opposite to n ⁺ -type ohmic contact layer 57. The absorber 64 is made of titanium, for example. The heat absorption pad 63 is arranged so as to contact the p-side ohmic contact electrode 62 on the side not connected to the n-side ohmic contact electrode 61. Further, the heat absorption pad 63 is arranged so as to contact the n-side ohmic contact electrode 61 on the side not connected to the p-side ohmic contact electrode 62. As a material constituting the heat absorption pad 63, for example, Au (gold) / Ti (titanium) is employed.

When the infrared sensor 51 is irradiated with infrared rays, the absorber 64 absorbs infrared energy. As a result, the temperature of the absorber 64 increases. On the other hand, the temperature rise of the heat absorbing pad 63 is suppressed. Therefore, a temperature difference is formed between the absorber 64 and the heat absorption pad 63. Then, in the p-type thermoelectric conversion material layer 59, p-type carriers (holes) move from the absorber 64 side toward the heat absorption pad 63 side. On the other hand, in the n-type thermoelectric conversion material layer 56, n-type carriers (electrons) move from the absorber 64 side toward the heat absorption pad 63 side. Infrared light is detected by taking out current generated as a result of carrier movement from the n-side ohmic contact electrode 61 and the p-side ohmic contact electrode 62.

In the infrared sensor 51 of the present embodiment, the ZT value is increased by increasing the conductivity as a material constituting the p-type thermoelectric conversion material layer 59 and the n-type thermoelectric conversion material layer 56. The thermoelectric conversion material of Form 1 is employed. As a result, the infrared sensor 51 is a highly sensitive infrared sensor.

In the thermoelectric conversion material, the base material that is a semiconductor is a SiGe-based material, a MnSi-based material, a SnSe-based material, and a Cu ₂ Se-based material. However, the present invention is not limited to this, and other semiconductors are used as the base material. Also good. For example, when the base material is formed using a group III-V element as a base material element, the number of electrons in the outermost shell of the second additive element and the number of electrons in the outermost shell of at least one of the base material elements The difference may be 1 as well. Also in this way, the efficiency of thermoelectric conversion can be improved.

In the thermoelectric conversion material, the state density of the first additional level may be a ratio of less than 0.1 with respect to the maximum value of the state density of the valence band adjacent to the forbidden band of the base material.

In the thermoelectric conversion material, the first additive element may be an element other than the transition metal.

In the above embodiment, the second additive element is preferably formed in a region within 0.1 eV from the valence band or conduction band of the base material. By doing so, it is possible to increase the carrier concentration even if the concentration of the second additive element is low, and therefore, it becomes easy to effectively move the Fermi level.

It should be understood that the embodiment disclosed herein is illustrative in all respects and is not restrictive in any way. The scope of the present disclosure is defined not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

1 Thermoelectric conversion material, 2 Crystal phase, 3 Amorphous phase, 5, 6a, 6b, 6c, 6d X-ray diffraction pattern, 10 Second additive element, 11 Valence band, 12 Conduction band, 13 Forbidden band, 14, 15 , 16 Addition level, 17a, 17b, 17c line, 21 π-type thermoelectric conversion element, 22, 52 p-type thermoelectric conversion material part, 23, 53 n-type thermoelectric conversion material part, 24 high temperature side electrode, 25 first low temperature side Electrode (low temperature side electrode), 26 second low temperature side electrode (low temperature side electrode), 27, 42, 43 wiring, 28 low temperature side insulator substrate, 29 high temperature side insulator substrate, 31, 32, 33, 34 end, 41 thermoelectric conversion module, 46a, 46b regions, 47 energy levels, 51 infrared sensor, 54 a substrate, 55 an etching stop layer, 56 n-type thermoelectric conversion material layer, 57 ^{n +} -type ohmic contact layer, 58 an insulator layer 59 p-type thermoelectric conversion material layer, 61 n-side ohmic contact electrode, 62 p-side ohmic contact electrode, 63 a heat absorbing pads, 64 absorbent body, 65 protective film, 66 recess

Claims

A base material which is a semiconductor composed of a base material element;
A first element that is an element different from the base material element, has a d orbit located inside the outermost shell, or a f orbit in the f orbit, and forms a first additional level in the forbidden band of the base material An additive element;
A second additive element that is different from both the base material element and the first additive element and forms a second additional level in the forbidden band of the base material,
The thermoelectric conversion material, wherein the difference between the number of electrons in the outermost shell of the second additive element and the number of electrons in at least one outermost shell of the matrix elements is 1.
The thermoelectric conversion material according to claim 1, wherein the structure of the thermoelectric conversion material includes a crystal phase composed of the base material element having a particle size of 50 nm or less.
In the X-ray diffraction pattern of the thermoelectric conversion material, the first additive element and the second additive element with respect to the intensity of the peak having the maximum intensity among the peaks indicating the crystal phase composed of the matrix element. The thermoelectric conversion material according to claim 2, wherein the ratio of the intensity of the peak having the maximum intensity among the peaks showing a crystal phase including at least one of them is 2.0% or less.
The ratio of the crystal phase containing at least one of the first additive element and the second additive element to the entire structure of the thermoelectric conversion material is 6.0% by volume or less. The thermoelectric conversion material according to claim 3.
The structure of the thermoelectric conversion material includes an amorphous phase mainly composed of the base material element,
The thermoelectric conversion material according to any one of claims 2 to 4, wherein a crystal phase composed of the base material element exists in the amorphous phase.
The thermoelectric conversion material according to any one of claims 1 to 5, wherein the first additive element is a transition metal.
The second additional level is a valence band or conduction band adjacent to the forbidden band of the base material, the energy band closer to the first additional level and the first additional level. The thermoelectric conversion material according to any one of claims 1 to 6, which is present in between.
The density of states of the first additional level has a ratio of 0.1 or more with respect to the maximum value of the density of states of the valence band adjacent to the forbidden band of the base material. The thermoelectric conversion material according to any one of the above.
The thermoelectric conversion material according to any one of claims 1 to 8, wherein a content ratio of the first additive element is 0.1 at% or more and 5 at% or less.
The base material is a SiGe-based material,
The ratio of the energy difference between the first additional level located closest to the valence band of the base material and the valence band of the base material with respect to the band gap of the base material is 20% or more,
The ratio of the energy difference between the first additional level located closest to the conduction band of the base material to the band gap of the base material and the conduction band of the base material is 20% or more. The thermoelectric conversion material according to any one of claims 1 to 9.
The thermoelectric conversion material according to claim 10, wherein the first additive element is Au, Fe, Cu, Ni, Mn, Cr, V, Ti, Ag, Pd, Pt, or Ir.
The first additive element is Au or Cu,
The thermoelectric conversion material according to claim 11, wherein the second additive element is B.
The first additive element is Fe;
The thermoelectric conversion material according to claim 11, wherein the second additive element is P.
The base material is a MnSi-based material,
The first additive element is Re or W;
The thermoelectric conversion material according to any one of claims 1 to 9, wherein the second additive element is Cr or Fe.
The base material is a SnSe-based material,
The first additive element is Sc, Ti or Zr,
10. The device according to claim 1, wherein the second additive element is F, Cl, Br, I, N, P, As, Sb, Bi, B, Al, Ga, or In. Thermoelectric conversion material.
The base material is a Cu 2 Se-based material,
The first additive element is V, Sc, Ti, Co or Ni,
The thermoelectric element according to any one of claims 1 to 9, wherein the second additive element is F, Cl, Br, I, N, P, As, Sb, Bi, Mg, Zn, or Cd. Conversion material.
A thermoelectric conversion material part;
A first electrode disposed in contact with the thermoelectric conversion material part;
A second electrode disposed in contact with the thermoelectric conversion material part and spaced apart from the first electrode;
The thermoelectric conversion element comprising the thermoelectric conversion material according to any one of claims 1 to 16, wherein a component composition of the thermoelectric conversion material portion is adjusted so that a conductivity type is p-type or n-type.
A thermoelectric conversion module including a plurality of thermoelectric conversion elements according to claim 17.
An absorber that absorbs light energy;
A thermoelectric conversion material part connected to the absorber,
The optical sensor comprising the thermoelectric conversion material according to any one of claims 1 to 16, wherein a component composition of the thermoelectric conversion material portion is adjusted so that a conductivity type is p-type or n-type.